CODEWITHSUNDEEP
phpmysqlmysqli
Arian Faurtosh
Arian Faurtosh

Reputation: 18521

How vital is $stmt->free_result()

$stmt = $mysqli->prepare("SELECT id, expire, status, username FROM username WHERE username= ?");
$stmt->bind_param('s', $username);
$stmt->execute();
// Store the result (so you can get the properties, like num_rows)
$stmt->store_result();
// Get the number of rows
$amountOfRows = $stmt->num_rows;

// Bind the result to variables
$stmt->bind_result($id, $expire, $status, $db_username);
// Process the variables
while($stmt->fetch()) {
    printf("%d %s %s %s\n", $id, $expire, $status, $db_username);
}

Do I need to add 

$stmt->free_result();

What about 

$stmt->close();

and

$mysqli->close();

QUESTION 1: I am guessing the answer is yes, but I want to know what each of these three do, so I can have a better understanding of how to use them.

I couldn't find much documentation that described what they do and why they are important.

QUESTION 2: My code run perfectly fine at face value, so what are the benefits to using these? Data Management, performance, security, SQL Injection... ?

Upvotes: 1

Views: 1958

Answers (1)

FalconC
FalconC

Reputation: 1436

Short answer: not vital.

Long answer: I thought the following commands free up memory:

$stmt->free_result();
$stmt->close();
$mysqli->close();

I wasn't sure, so I tested it.

echo(memory_get_usage());  // returns 226472

$mysqli = new mysqli(/* credentials */);
$stmt = $mysqli->prepare("SELECT id, username FROM members");
$stmt->execute();
$stmt->store_result();
$amountOfRows = $stmt->num_rows;
$stmt->bind_result($id, $username);

while($stmt->fetch()) {
    printf("%d %s\n", $id, $username);
}

echo(memory_get_usage());  // now returns 230176 (gained 3704)

$stmt->free_result();
echo(memory_get_usage());  // returns 230176 (lost 0)

$stmt->close();
echo(memory_get_usage());  // returns 229816 (lost 360)

$mysqli->close();
echo(memory_get_usage());  // returns 229720 (lost 96)

$stmt->close() and $mysqli->close() actually free up memory, but it is a tiny bit.

Your system won't be any more vulnerable because you choose not to write these two/three lines. They only free up (little) memory. It is arguably better style to include at least $mysqli->close() in your code, but it's up to you.

Verdict: not vital.

Upvotes: 2

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